The present invention concerns a support comprising at least two dealuminated Y zeolites associated with a matrix which is normally amorphous or of low crystallinity, a catalyst containing that support, its use in conventional hydroconversion of petroleum cuts and a hydroconversion process using the support.
Conventional hydrocracking of heavy petroleum cuts is a process which is very important in refining which produces, from surplus and heavy feeds of low upgradability, lighter fractions such as gasolines, aviation fuel and light gas oils which the refiner needs in order to adapt his production to demand. In comparison with catalytic cracking, catalytic hydrocracking is important for the production of very high quality middle distillates, aviation fuels and gas oils. In contrast, the gasoline produced has a much lower octane number than that from catalytic cracking.
The catalysts used in conventional hydrocracking are all bifunctional, associating an acid function with a hydrogenating function. The acid function is provided by supports with large surface areas (generally 150 to 800 m.sup.2.g.sup.-1) with a superficial acidity, such as halogenated aluminas (in particular chlorinated or fluorinated aluminas), combinations of boron oxides and aluminium oxides, amorphous silica-aluminas and zeolites. The hydrogenating function is provided either by one or more metals from group Vm of the periodic table, such as iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum, or by the association of at least one metal from group VI of the periodic table, such as chromium, molybdenum and tungsten, and at least one group VIII metal, preferably a non-noble metal.
The balance between the two functions, acid and hydrogenating, is the fundamental parameter which governs the activity and selectivity of the catalyst. A weak acid function and a strong hydrogenating function results in catalysts of low activity which generally work at a high temperature (390.degree. C. or more) and at a low space velocity (HSV, expressed as the volume of feed to be treated per unit volume of catalyst per hour, generally less than 2), but have very good selectivity for middle distillates. Conversely, a strong acid function and a weak hydrogenating function results in very active catalysts with, however, poor selectivity for middle distillates. The operator's problem is thus careful choice of each of the functions to adjust the activity/selectivity couple of the catalyst.
Thus it is very important in hydrocracking to have great flexibility at various levels: flexibility in the catalysts used, which provides flexibility in the feeds to be treated and in the products obtained. One parameter is the acidity of the catalyst support.
The great majority of conventional catalytic hydrocracking catalysts contain weakly acidic supports, such as amorphous silica-aluminas. Such systems are used to produce very high quality middle distillates and, when of very low acidity, oil stock.
Amorphous silica-aluminas form a family of low acidity supports. Many commercial hydrocracking catalysts are constituted by silica-alumina associated with either a group VIII metal or, as is preferable when the quantity of heteroatomic poisons in the feed to be treated exceeds 0.5% by weight, with an association of sulphides of metals from groups VIB and VIII. Such systems have very good selectivity for middle distillates and the products formed are of high quality. The least acidic of such catalysts can also produce lubricant stock. The disadvantage of all of these catalytic systems based on an amorphous support is, as has already been stated, their low activity.